Golfdom, April 2018

Super Science Continued from page 33 factors grass cultivar air movement fertility irrigation etc that affect the onset of symptoms Instead superintendents need to set the model spray threshold appropriate for their course This threshold is the chosen probability at which the user will make applications which means the model is adaptable for different micro environments However choosing an individual threshold may require a little experimentation ESTABLISHING PROBABILITY THRESHOLDS Research carried out at Wisconsin established an effective threshold of 20 percent probability which users can tweak until its most efficient for a particular situation This original threshold was determined from Penncross creeping bentgrass Agrostis stolonifera L in a more northern climate so thresholds chosen across other locations may differ Figure 2 This threshold value worked well in numerous climates including Pennsylvania New Jersey Oklahoma Mississippi and Tennessee However turfgrass managers can adjust the threshold based on cultivar location and amount of risk they are willing to accept The 20 percent threshold worked as well as applying fungicide every two weeks through the summer months and normally resulted in saving one to two fungicide applications Once youve determine a threshold spraying is appropriate any time the threshold is met Once youve sprayed and you know your interval of expected suppression another application is not necessary until the suppression interval is met and the advisory predicts onset of disease At the end of the suppression interval revisit the model If the threshold is met on the day the spray interval has passed another fungicide application is in order If the threshold has not been met spraying is not necessary FIGURE 3 35 30 25 20 15 10 5 0 Dollar Spot Model Probability 1st Fungicide Application Made 2nd Fungicide Application Made 28 Day Spray Interval Ignore Model Output 20 spray threshold Smith Kerns Model Output 5 1 5 8 5 15 5 22 5 29 6 5 6 12 6 19 6 26 7 3 This figure depicts how the Smith Kerns Model works in practice The length of residual control is determined by the product used and from the expectation of the golf course superintendent Figure 3 This way you could reduce applications or extend the period between some fungicide applications Conveniently for users of the model multiple online tools are available to calculate dollar spot event probabilities Paul Koch Ph D at the University of Wisconsin Madison has compiled a thorough page on his labs website https tdl wisc edu dollar spotmodel outlining model details providing links to online tools and offering downloads of easy to use Excel spreadsheets for both Fahrenheit and Celsius temperatures The downloaded spreadsheet will appear with numbers already populated once opened demonstrating its utility and making it easy to follow and adjustable for the individual user For each day average relative humidity and the daily high and low temperatures are all you need to calculate dollar spot probability with the Smith Kerns Model This example illustrates that you use the first five days to create the running averages so a probability of dollar spot occurrence will not be created with the Smith Kerns Model until the fifth day of data This doesnt mean you have to wait for the spreadsheet to be helpful because obtaining this past data through any weather service makes this tool immediately useful to superintendents There also are two sites from which you may access and use the Smith Kerns Model GDDTracker of Michigan State University found at gddtracker net and the GreenKeeper App from Bill Kreuser Ph D at the University of Nebraska Lincoln found at greenkeeperapp com The model also is available on uspest org THE POINT IS ELIMINATING APPLICATIONS Based on the model work conducted in Wisconsin Oklahoma and elsewhere superintendents can expect to save a modest number of fungicide applications while maintaining the same level of disease control A twoyear study using the model at the O J Noer Turfgrass Research Facility in 34 Golfdom April 2018 Golfdom com

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